For the material-bonded joining of metal sheets or similar workpieces, both fusion and pressure welding methods may be used.
In the case of fusion welding methods, a common molten pool of the two parts being connected is created, with the optional addition of a filler material, usually in the form of a welding wire. This is followed by the creation of a pool solidification structure. The thermal loading of the components in the joining region is equivalent to the melting temperatures of the materials to be joined.
In the case of pressure welding methods, apart from the heating by various heat sources, such as for example electrical resistance heating, the material is brought to the softening temperature and pressed together by a pressing force, whereby a welded connection is created.
In the case of the known friction stir welding, the materials to be connected are heated by a stirring process and intermixed in the welding region. However, this method is limited to specific materials that deform well and to minimum material thicknesses.
In the case of cold pressure welding, there is likewise a restriction to softer materials and specific material thicknesses.
The joining of thin-walled workpieces, in particular the joining of metal sheets, requires special measures, since the volume of material that is made available by the workpieces in the joining region is very small and since damage to the adjacent regions of the metal sheets must be avoided. It has therefore already been proposed in the case of friction welding methods for joining thin-walled metal tubes to other bodies to widen the periphery of the metal tube before the friction welding in order to prevent notching. This is described in DE 38 02 300 C1. Another method, in which the contact zone is made as large as possible with a frictional tool, is shown by EP 1 236 533 A1.